By Ken Freund
August 26, 2016
Filed under RV Tech Q&A
I own a 26½-foot Class C motorhome that has been experiencing tire failures. I weighed it on a truck scale, and the front axle weighs 1,810 pounds on the left and 1,930 pounds on the right. The left rear weighs 4,000 pounds on the axle and the right weighs 4,050 pounds, for a total rear weight of 8,050 pounds. I have Michelin LT225/75R16 tires on it, which are dual rated for a total of 9,880 pounds, so the tires are actually 1,830 pounds under their limit. Why are these tires coming apart after just 4½ years? Is there a stronger tire I can put on this motorhome?
Kent Williams | Hesperia, California
I don’t think it’s a matter of finding a “stronger” tire. Michelin makes good tires, and most owners have good experiences with them. First, we need to determine what caused the failure. You didn’t mention what model tires you have, or which positions failed, or if you had multiple failures in the same position. Did you base the age on how long you had the tires, or on the dates embossed on the sidewalls? While you may have only had them for 4½ years, the tires may have sat in a warehouse for years. The area of high desert where you live has very strong sunlight, a lot of extremely hot days and a high ozone concentration, a combination which is deadly for rubber. Most tire failures are caused by under-inflation, which may be caused by a slow leak from a puncture, leaky valve stems, bead leaks, curb or pothole impacts, or simply from air escaping through the porosity of the rubber. Often the inner tires are low and are less likely to get noticed. If you still have the tires, I suggest you take them to a tire expert for examination. I also suggest you invest in a tire-pressure-monitoring system to keep an eye on tire pressure, and you should also carry a portable air compressor that will handle the pressure to top them off when needed.
This is regarding Terry Bush’s “Workhorse Intermittent Limp Home Mode” letter in July. I am a retired trucker with more than a million miles of driving experience. On one of my highway runs, I suffered the same malady as Bush, where the unit would go to the limp-home mode, except in my case the unit went to idle. Luckily, I was going fast enough to safely move over to the shoulder of the interstate. The engine would idle but not accelerate despite stopping/starting the Cummins engine, turning everything off/on and the batteries being fully charged. After going through everything I could think of, the engine responded and I was able to continue on to our nearest terminal.
Then the accelerator pedal failed to respond. I discovered that I could accelerate the engine by using the cruise +/- switch, though there was no response from the pedal. Thus I was able to drive to the nearest repair shop. At the shop, the diagnostic computer reported that the problem was a throttle position sensor (TPS) fault. The TPS is merely a roller assembly and thus nothing about that device can really go wrong. More sleuthing disclosed that the cable through which the TPS signaled the computer to respond to pedal input had worn through the insulation, grounding the TPS, and the computer determined that to be idle. While I do not recommend using the cruise control +/- in normal operation, this tidbit may help someone in a similar position when all else appears normal.
Doug Siskow | New Braunfels, Texas
Thanks for sharing your experience and tip. As the old saying goes, “If you can’t fix it with a rock or a hammer, you have an electrical problem.” When electronics work, everything is great, but when they fail it can be frustrating. A lot of good parts get thrown away because trouble codes refer to the component, when it can also be the connections and wires gong to it.
ABS Light On
I, too, had an ABS light that stayed on all the time (“ABS Malfunction,” February). When I was at a Ford dealer for an oil change on my motorhome, they told me they had to replace a missing fuse for the ABS circuit. The mechanic noticed the light when he moved the vehicle. I had assumed that the constant light was telling me that it was active, not that it wasn’t working. Apparently, someone forgot to install it at the factory.
Natalie Pope | Lakeland, Florida
Thanks for writing; this brings up several points I’d like to make. The automotive industry’s standard for many years has been for warning lights to be in red, while normal indications are usually in green or not lighted at all except for test on start-up. Every RVer should become familiar with ALL of their vehicle’s dash-panel functions, lights, gauges and warning systems, and their operation. The owner’s manual covers this information in detail and is included in every vehicle when it comes from the factory. Many are also available online at the manufacturer’s website for free.
Another important thing for owners to do is familiarize themselves with the actual operation of their ABS braking system during a “panic” stop. Many drivers become startled by the pulsing pedal and actually release it rather than continue pressing the pedal to allow the ABS to do its job. A good place to try this is in an empty, open dirt or sand-covered parking lot. Make sure everything is secured inside the motorhome (it always should be anyway when driving because you never know when fast braking or quick maneuvers may be required) so nothing goes flying. Try first at a low speed and perhaps build up to, say, 25 mph or so if safe space allows.
Vinyl Flooring Tip
In the June issue, you had a letter about vinyl floor cracking while in storage (“Torn Vinyl Flooring”). The reader indicated that he had the problem when he changed parking areas. Speaking professionally as a wood technologist, I can offer the following explanation.
An RV is most likely built at 40 percent relative humidity (RH), so all the wood is at 8 percent moisture content (MC); this is also the typical interior environment when we are living in the RV, so it’s a good choice for the manufacturer.
Now consider long-term storage of an RV. The outdoor environment in most of the United States and Canada is around 65 percent RH, so during long storage periods, the wood or wood composite floor and the wood inside the RV will increase to about 12 percent MC, assuming the ground underneath is paved and well-drained, or the RV is stored in a windy location away from large bodies of water.
What this slightly higher (compared to 40 percent RH or 8 percent MC) moisture in storage means is that the wood flooring, wood cabinets and wood furniture will increase in MC and therefore expand slightly.
However, we might notice that after storage, sometimes the cabinet doors are tight or molding pieces are slightly buckled because of this expansion. This expansion is tolerated by a new and warm floor, as new, warm vinyl is soft and pliable. This is for normal storage.
But consider what happens during storage of an RV if it is parked on grass or in a poorly drained site. At such a location, the circulation of air beneath the RV is lower than normal and the humidity under the RV can often increase to nearly 100 percent RH. This high humidity encourages odors, mildew, mold and even rot and rusting. But even more importantly, especially in the wintertime, the wood floor will swell or try to swell as much as 2 percent. It does take time for this to happen, so that is why driving through rain does not cause an issue.
The wood cabinet doors will swell even more and potentially become tighter and perhaps misaligned. As the floor swells, the vinyl stays the same size, and in the cold, the flooring especially can be quite brittle. So as the floor expands in storage in a moist location and puts tension on the vinyl, cracks can develop, especially in older RVs where the vinyl has become brittle. Further, sometimes the frame of the RV restricts expansion, so the wood flooring will buckle slightly and, when it dries, may squeak. Also, when the floor dries and shrinks later in the year, the fasteners will often protrude and can be seen as a slight bump on the vinyl floor.
How can we prevent these types of problems? Avoid trapped air under the RV in storage (keep it ventilated), and avoid locations with damp soil underneath. Consider putting a sheet of plastic under the RV to block soil moisture, and make sure that an RV cover is securely attached to the RV while still allowing the air beneath the RV to move freely. Finally, add a little heat (20 to 25 degrees Fahrenheit above the average outside temperature) to the inside of the RV during storage, as heat lowers the humidity.
Eugene Wengert, The Wood Doctors Rx | Bishop, Georgia
Thanks for sharing your expertise with us, Eugene. This makes perfect sense in explaining what is happening to the materials in a motorhome. Your suggestions about storage are also useful for those in moist climates.